UK researchers from the University of Manchester are experimenting with 3D printing techniques for bioprinting, with their findings recently published in ‘Three-Dimensional Printing and Electrospinning Dual-Scale Polycaprolactone Scaffolds with Low-Density and Oriented Fibers to Promote Cell Alignment.’
As bioprinting and tissue engineering continue to be the focus of scientists in labs around the world eager to 3D print organs that can be successfully used for patient-specific treatment, a wide range of fascinating projects have emerged, from bioprinting for stem cell research to a variety of different new materials and structures for scaffolds. In this study, the authors are focused on fabricating electrospun scaffolds, aligning nanoscale fibers for improved cell viability.
With the opportunity to integrate fibers that are suitable for imitating the extracellular matrix (ECM), the researchers were able to fabricate a 3D printed network of fabricated and electrospun micro- and nanofibers, providing:
- Mechanical stability
- Interconnectivity
- High porosity
- Large surface to volume ratio
- Good cell attachment potential
Sustainability of cells is the greatest challenge for researchers involved in tissue engineering, but here the authors were encouraged due to the generous surface area offered for both attachment and bridging of fibers, able to create a successful microenvironment for cells to interact and move.
With proper modulation of cell behavior, many positive features were offered
- Specific cell adhesion
- Morphology
- Migration
- Proliferation
- Polarity
- Integrin clustering
- Differentiation
“Electrospinning oriented fibers can be achieved through a number of techniques such as using a rotating mandrel collector, conductive electrodes separated by an insulating gap, a patterned collector, and near-field electrospinning,” explained the authors. “The ECM in most tissues has an anisotropic architecture, thus the fabrication of aligned fibers is key to mimicking the native structure and has a significant effect on cell behavior and tissue regeneration.”
Using a 3D Discovery, screw-assisted extrusion 3D printer and an electrospinning system, the research team made dual-scale scaffolds with PCL, featuring a 0°/90° lay down, 300 μm pore size and fiber diameter, and 230 μm layer height. Processing parameters were as follows: .33 mm inner diameter (ID) nozzle, 90°C melt temperature, 12 mm/s deposition speed, and screw rate of 7.5 rpm. Fifteen sample scaffolds were printed.
Schematic representation of the 3D printing and electrospinning fabrication process of a dual-scale scaffold. 3D, three-dimensional.
With a diameter of 820 ± 56 nm, electrospun fibers were integrated onto scaffolds, with beads displayed on the fibers and also in the pores. The researchers attributed the beads to possible issues with conductive properties, decrease in charge, or use of solvents. They did note that on the meshes fiber alignment was exhibited on those spun for 30 seconds or more.
SEM images of the (a) 3D-printed only scaffold and (b) dual-scale scaffold with electrospun (45 s) nanofibers (scale bar = 300 μm). Electrospun mesh density as function of time (c) 15 s, (d) 30 s, (e) 45 s, and (f) 120 s [scale bar = 20 μm, (e) 50 μm]. SEM, scanning electron microscopy.
“The aligned fibers are present and homogeneously distributed throughout and within all the 3D-printed pores,” stated the researchers. “Furthermore, the electrospun fibers collected on the printed fibers themselves are oriented although not as clearly as the fibers within the pores.”
Fiber orientation analysis of SEM images. (a) Low magnification image showing aligned electrospun fibers (45 s) within all the pores of the printed scaffold (scale bar = 300 μm). Probability density of the orientation angle (relative to x-axis) shows a distinct distribution for angles between 75° and 90°. Higher magnification images (b) 45 s (scale bar = 50 μm) and (c) 120 s (scale bar = 20 μm) show aligned fibers with the orientation angle distributed toward 0°. Color images are available online.
“Further investigation is required to understand how the conductivity of the material influences fiber formation and alignment potentially through the incorporation of conductive fillers such as graphene or the use of conductive polymers. The electrical charge distribution can also be altered by changing the printed scaffold geometry (e.g., hexagonal and triangular) and incorporating both conductive and insulating regions within the structure to influence fiber alignment,” concluded the researchers. “This study is a promising development in the fabrication of multiscale scaffolds that better reflect the complexity of native tissue and the ability to engineer specific architectures to control cell behavior.”
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